Frequency multiplier circuit



Dec. 29, 1953 J. s. Russo FREQUENCY MULTIPLIER CIRCUIT Filed Oct. 12, 1950 III lNvENToR Jjm Si 12,950

ATTO RN EY and is connected through a Patented Dec. 29, 1953 attesi@ UNITED STATES PATENT oFFIcE FREQUENCY MULTIPLIER CIRCUIT John S. Russo, Philadelphia, Pa., assigner to Radio Corporation of America, a. corporation of Delaware lApplication October 12, 1950, Serial No. 189,728 4 claims. (c1. 25o-36) This invention relates to a frequency multiplier circuit, and more particularly to aA kcircuit for producing a frequency which is a given multiple or harmonic of a fundamental input frequency.

An object of this invention is to devise a frequency multiplier which has particular utility at frequencies in the low radio frequency range.

Another object is to devise a frequency multif plier which has very high selectivity for the desired harmonic frequency.

A furtherobject is to provide a frequency -multiplier circuit which has extreme flexibility of loading.

An additional object is to provide a frequency multiplier of small physical size, which small size vis of importance in portable equipment.

The foregoing and lother objects of the inven- ,tion will be best understood from the following :description of an exemplication thereof,refer lence being -had to the accompanying drawing whose single figure diagrammatically represents a frequency multiplier circuit according to this invention.

, The objects of this invention are accomplished,

brieily, in the following manner: A parallel inductance-capacitance. (LC) resonant Icircuit,

,tuned to the desired harmonic, is shock-excited ,by the fundamental frequency. A small coil is inductively coupled to the coil of this circuit, and

is connected by means of a transmission line to a series LC circuit tuned to the desired harmonic, from which series circuit output of harmonic ,frequency may be taken, via a capacitive voltage ,divider if desired.

Referring to the drawing, a source of funda- 'rf vmental input frequency I having a frequency f fis coupled through a condenser 2 to the control positive terminal of a source of unidirectional potential.

A parallel resonant LC circuit I0, consisting of an inductance or coil II and a capacitor I2, is connected in the output circuit of tube 4, between anode I3 thereof and a source of positive potential. Circuit IIl is tuned to the desired harmonic of the input frequency f, for example, to 5 f lor Gf. As a typical example, although this invention 1s not to be considered limited in any way thereby,

the frequency f may be' 93.109 kc. In this case, then, circuit II] may be tuned to approximately 465km Vor to approximately 558 kc., depending on whether` the iifth or sixth harmonic is desired. Application of the fundamental frequency f to grid 3 provides shock excitation in the circuit I0, thus providing harmonic frequency voltage in coil II. The Q of circuit IG is made high to reduce as much as possible the damping of the harmonic frequency voltage between cycles of the input fundamental frequency. n

The `circuit of this invention has particular application to harmonic frequencies in the low radio frequency range, such as those given by such coil will ordinarily consist of only a few without considering the turns of wire on a core having a large amount of iron. Conventionally, frequency multipliers hav- `v ing high selectivity for the desired harmonic frequency require double tuned circuits, or, in other Words, require that the coil of another tuned circuit (tuned to the desired harmonic frequency) be coupled to coil II of tuned 1circuit l0. Such a coil to 'be inductively coupled to coil I I must also have a large inductance, if its tuned circuit is to be tuned to a harmonic frequency on the order of 500 kc., for example. Also, to be efiicient in operationsuch a coil to be coupled t-o lcoil II would -have to have a high Q. It is extremely diincult to couple directly two coils of large inductance, and

it is particularly so if these coils are both of high Q. which means in the present circuit a few turns of wire on a rather large iron core. According .to the present invention, double tuned circuits, re-

'-quiringv large inductances' when used in the low `radio frequency range, are rendered unnecessary.

Coils having large inductances can be used in this invention, without worrying about the diiiiculties of coupling two such coils to each other. Also, by the present invention, coupling to the parallel resonant shock-excited circuit IE? can be effected problems of directly couplingjwo high-Q coils. l `The aux developed 111.0011 Il links e con la, which is inductively coupled thereto. Coils II and I3 may be enclosed in the same casing or shell, indicated by the dotted rectangle I4. Coil i3 .does not need to have a high Q, nor does it need to have a high value of inductance. Therefore, it can be very easily and simply coupled to coil I I, and may in fact consist of merely a few turns of wire Wound on the same core as is coil I i. The coupling between coils II and I3 may be adjusted to be as tight or as loose as desired.

One end of coil I3 is grounded as indicated and its opposite end is connected by means of a trans'- rnission line or link I5 to one end of a coil I6. Line I5 may be any suitable form of line, such as an open wire line or a coaxial transmission line, the latter being preferable if it is desired to reduce radiation from the line. The inductances of coils I9 and II are both large compared to that of coil I3, and coil I6 is designed to havefa very high Q. Coil Iii may be mounted inside a casing or shell, indicated by the dotted rectangle Il.

The other end of coil I6 is connected through aV capacitive voltage divider, consisting of two series-connected capacitors I8 and I9, to ground. Therefore, the harmonic frequency voltage developed across coil I3 is applied to the series circuit I.6, I8, I9. The series LC circuit I6, I8, I9 is tuned to the desired harmonic frequency, this circuit being therefore a harmonically-tuned series resonant circuit. Output of harnfonic frequency nf, where n is the desired multiplication factor, may be taken from across capacitor I9 byV means of a pairof leads 2a connected thereacross.

In addition to providing a capacitive voltage divider, the combination of capacitors I8 and I9 serves another useful purpose. The capacitance of I9 may be large compared to that of I8. Therefore, variations in the capacity of .a tube, to which leads 20 might be connected, have an almost negligible effect on the frequency to which circuit IS,.I8, I9 is tuned, since they have van. almost negligible effect on the resultant or i total capacitance of the two series-connected capacitors I8 and I9.

The voltage across the series combination of the two capacitors I8 and I9 will be approximately equal to the voltage across coil I3 multiplied by the Q of coil I6. Since both of these factors can be, and preferably are, quite high, high output voltage at the desired harmonic frequency nf will be delivered by leads 2i). This output voltage will be free from appreciable modulation of the exciting voltage of frequency f, due in part to the fact that the coils II and I6 each have high Q.

VThe series resonant circuit I6, I8, I9 has a low impedance at the harmonic frequency, since it is tuned to such frequency. The choice of the impedance of transmission line I5'is the factor which determines the length of such line. Ordinarily, .the impedance of transmission line I5 matches the resonant impedancerof'circuit' I 6, I8, I9, Which is quite low at the-harmonic frequency. vConditionsof mismatch, at low frequency, cause the line I5 to act as a shunt capacitance. This has the effect of detuning the I6, I8, I9 circuit. However, this detuning can be compensated for by an adjustment of inductance I6; therefore, the link I5 connecting I3 and I6 may be of considerable length, if desired. The fact that the link I5 may be of considerable length, enables extreme flexibility of loading of the arrangement of this invention. Inrother words, the load'may be separated a considerable distance from the main part of the circuit, including tube 4 and circuit III.

Since coils II and I6 may each have high inductance and high Q, the circuit of this invention has particular utility at frequencies in the low radio frequency range. Due to the use of two resonant circuits, to wit, theparallel resonant circuit I0 and the series resonant circuit I6, IS, I9, both tuned to the harmonic frequency, high selectivity is provided for the desired harvmonic frequency. The entire arrangement is of small physical size, due in part to the fact that the high-Q coils II and I6 do not need to be directly coupled together; such direct cou pling would necessarily increase the physical size of the system.

What is claimed is:

1. A frequency multiplier circuit comprising a parallel resonant circuit narrowly tuned to the single desired output frequencynneans for shock exciting said circuit with a frequency which is a sub-multiple of said output frequency, a coil coupled inductively to said circuit, a vresonant circuit narrowly tuned to said single output frequency, output connections coupled to said'lastnamed resonant circuit, and means for connecting said last-named resonant circuit across said coil through connections devoid of concentrated impedance.

2. A frequency multiplier circuit comprising a parallel resonant circuit narrowly tuned to the single desired output frequency, means for shock exciting said circuit with a frequency which is a sub-multiple of said output frequency, a coil coupled inductively to said circuit, a series resonant circuit narrowly tuned to said single output frequency, output connections coupled to said series circuit, and means Vfor connecting said series circuit across said coil through connections devoid of concentrated impedance.

v3. A frequency multiplier circuit comprising a resonant circuit narrowly tuned to the single desired output frequency, means for shock exciting said circuit with a frequency which is a submultiple of said output frequency, a coil coupled inductively to said circuit, a series inductancecapacitance resonant circuit narrowly tuned to said single output frequency, the capacitance of said series circuit comprising a plurality'of capacitors constituting a voltage divider, an output circuit coupled across a portion of said divider, and means for connectingI said series circuit across said coil through connections devoid of concentrated impedance.

4. A frequency multiplier circuit in accordance with claim 3, wherein the portion of the divider across which the output circuit is coupled includes a capacitor having a capacitance which is large 'compared to the capacitanceof the remaining ones of the plurality of capacitors.

JOI-IN S. RUSSO.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,646,439 Aifel Oct. 25, 1927 2,266,668 Tubbs Dec. 16, 1941 2,368,780 Roberts Feb. 6, 1945 .2,484,763 Sturm Oct.1l, 1949 

